The invention relates to a method of making a colour selection deflection structure for a colour picture display tube comprising a channel plate electron multiplier provided with an extractor electrode mounted on and electrically insulated from the output face of the electron multiplier. The invention also relates to a colour picture display tube which includes a colour selection deflection electrode structure manufactured by such a method.
Colour picture display tubes have been proposed which include a laminated dynode channel plate electron multiplier provided with an apertured extractor electrode mounted on and electrically insulated from the output face of an electron multiplier and use a single electron gun to produce colour pictures. It has been found possible both to improve the colour quality of the pictures and to make corrections for small misalignments between the channel plate electron multiplier and the phosphor patterns on the display screen. This has been achieved by providing the tube with a colour selection deflection structure in which pairs of deflection electrodes are disposed between columns of apertures in an extractor electrode provided on the output side of the channel plate multiplier. Specification GB-A-2,124,017 discloses such a picture tube which comprises a laminated dynode channel plate electron multiplier, means for generating an electron beam to be scanned across an input face of the electron multiplier, an apertured extractor electrode mounted on and electrically insulated from an output face of the electron multiplier, apertures in the extractor electrode communicating with respective channels in the electron multiplier, a luminescent screen spaced from the extractor electrode, the screen comprising a repeating pattern of phosphor elements adapted to luminesce in different colours, each pattern comprising one of each type of phosphor only and, between apertures of the extractor electrode, pairs of first and second deflector electrodes electrically insulated from each other and the extractor electrode, the first electrodes of each pair being coupled together and the second electrodes of each pair being coupled together, wherein the apertures in the extractor electrode are arranged rectilinearly and a pair of first and second electrodes is disposed between adjacent lines of the apertures. The use of pairs of first and second deflector electrodes between adjacent lines of apertures in the extractor electrode enables electrical corrections to be made for static misalignment errors.
Specification GB-A-2,124,017 describes a method of making the deflection electrode structure, in which method elongate slots are etched in a plate of FOTOFORM (Registered Trade Mark) glass which is electrically insulating, between margins of the plate. The width of the slots corresponded substantially to the distance between the facing surfaces of a pair of deflector electrodes arranged one on each side of a row of apertures in the extractor electrode. Electrically conductive material is then evaporated onto one main surface of the etched plate and down onto the sidewalls of the slots. The electrically conductive material is present on areas of the main surfaces of the plate and on the sidewalls. Where it is not required it is subsequently removed to leave the desired electrode structure. Care is taken to ensure both that all the electrode elements of each respective set remain interconnected and to avoid short circuits between electrode elements of the two sets or between an electrode element of one set and an interconnecting strip of the other set.
An object of the invention is to provide a cheap and simple method of making a colour selection deflection structure for a colour picture display tube which includes a channel plate electron multiplier. Another object of the invention is to provide a colour display picture tube with a colour selection deflection structure which is electrically robust, so that, for example, there would be no failure of this structure in the event of a flashover.